At the present time, solvent-dominated recovery processes (SDRPs) are rarely used to produce highly viscous oil. Highly viscous oils are produced primarily using thermal methods in which heat, typically in the form of steam, is added to the reservoir. Cyclic solvent-dominated recovery processes (CSDRPs) are a subset of SDRPs. A CSDRP is typically, but not necessarily, a non-thermal recovery method that uses a solvent to mobilize viscous oil by cycles of injection and production. Solvent-dominated means that the injectant comprises greater than 50% by mass of solvent or that greater than 50% of the produced oil's viscosity reduction is obtained by chemical solvation rather than by thermal means. One possible laboratory method for roughly comparing the relative contribution of heat and dilution to the viscosity reduction obtained in a proposed oil recovery process is to compare the viscosity obtained by diluting an oil sample with a solvent to the viscosity reduction obtained by heating the sample.
In a CSDRP, a viscosity-reducing solvent is injected through a well into a subterranean viscous-oil reservoir, causing the pressure to increase. Next, the pressure is lowered and reduced-viscosity oil is produced to the surface through the same well through which the solvent was injected. Multiple cycles of injection and production are used. In some instances, a well may not undergo cycles of injection and production, but only cycles of injection or only cycles of production.
CSDRPs may be particularly attractive for thinner or lower-oil-saturation reservoirs. In such reservoirs, thermal methods utilizing heat to reduce viscous oil viscosity may be inefficient due to excessive heat loss to the overburden and/or underburden and/or reservoir with low oil content.
References describing specific CSDRPs include: Canadian Patent No. 2,349,234 (Lim et al.); G. B. Lim et al., “Three-dimensional Scaled Physical Modeling of Solvent Vapour Extraction of Cold Lake Bitumen”, The Journal of Canadian Petroleum Technology, 35(4), pp. 32-40, April 1996; G. B. Lim et al., “Cyclic Stimulation of Cold Lake Oil Sand with Supercritical Ethane”, SPE Paper 30298, 1995; U.S. Pat. No. 3,954,141 (Allen et al.); and M. Feali et al., “Feasibility Study of the Cyclic VAPEX Process for Low Permeable Carbonate Systems”, International Petroleum Technology Conference Paper 12833, 2008.
The family of processes within the Lim et al. references describe embodiments of a particular SDRP that is also a cyclic solvent-dominated recovery process (CSDRP). These processes relate to the recovery of heavy oil and bitumen from subterranean reservoirs using cyclic injection of a solvent in the liquid state which vaporizes upon production. The family of processes within the Lim et al. references may be referred to as CSP™ processes.
Solvent-dominated recovery processes (SDRP)s may involve the addition of hydrocarbon solvents (such as propane) to an underground oil reservoir, including a reservoir of viscous oil such as bitumen, to mix with and lower the viscosity of the bitumen, and allow it to be produced. The hydrocarbon portion of the produced mixture includes the solvent and produced oil, in a vapor phase and one or more liquid phases. Depending on the particular pressure and composition, the liquid portion can be in two liquid phases. Previously described SDRPs, such as CSP™ technology, an example of which is described in Canadian Patent No. 2,349,234, involve flashing the solvent in the entire produced mixture, leaving a single produced oil phase. The solvent may then be re-injected into the reservoir.
Whereas in such SDRPs, the solvent is present in the oil stream, in certain instances outside the field of In situ oil recovery, oils are refined through the addition of a solvent, which solvent is then removed from the refined oil. Solvent deasphalting in a refinery environment is known. For instance, U.S. Pat. No. 4,125,458 describes a process to simultaneously deasphalt-extract a mineral oil feedstock comprising both asphaltene and aromatic components. Suitable feedstocks are said to include whole crude oils, atmospheric and vacuum residua, and mixtures thereof having initial boiling points ranging from 500 to 1,100° F. at atmospheric pressure. The feed is contacted with a deasphalting-extraction solvent in one or more mixer-settler units or in one or more countercurrent liquid-liquid converting towers. The solvent is then flashed off from the mixture.
The following four references also relate to the use of solvent to purify an oil feed. U.S. Pat. No. 6,174,431 relates generally to the recovery and regeneration of used lubricant and industrial oils and more specifically to the treatment and refinement of used lubricants and industrial oils to produce re-refined base oil and to remove additives and impurities from used oils and lubricants. A pre-treated used oil may be combined with liquid propane and an extraction vessel and a settling vessel may be used to produce a heavy fraction and a light fraction. The propane may be removed independently from each of these fractions.
U.S. Pat. No. 4,169,044 describes a process for re-refining used lubricating oil. The used lubricating oil is subjected to a solvent extraction in a first extraction zone with a light hydrocarbon solvent to separate a solvent-rich extract oil fraction from a solvent-lean bottoms fraction. Substantially purified lube oil is recovered from the solvent-rich extract oil fraction. The solvent-lean bottoms fraction is subjected to a solvent extraction in a second extraction zone with the light hydrocarbon solvent at a higher solvent-to-oil liquid volume ratio than that of the first solvent extraction to thereby separate a second solvent-rich extract oil fraction from a second solvent-lean bottoms fraction. The substantially purified heavy oil from the second solvent-rich extract oil fraction is recovered. Finally, all remaining solvent from the solids in the second solvent-lean bottoms fraction is removed.
In the field of In situ oil recovery, U.S. Pat. No. 4,476,928 relates to the tertiary recovery of subterranean hydrocarbons using a solvent, and more particularly to a method and apparatus for the generation of a solvent by the recovery of ethers and other light ends from a liquid mixture of organic compounds recovered from the subterranean deposits. Ambient air is bubbled through liquid hydrocarbons in a storage tank to evaporate or boil off light ends which may be used as solvent for injection into the subterranean oil field or coal deposit. The solvent may be used to provide a gas drive or as an extraction solvent for the recovery of crude oil.
U.S. Patent Application Publication No. US 2009/0242463 relates to a continuous process for upgrading a heavy hydrocarbon. The heavy hydrocarbon is heated and contacted with a solvent to form a first product comprising a mixture of upgraded hydrocarbons and solvent, and a second product comprising asphaltene waste and water. Solvent is recovered from each of the first and second products.
Mixing solvent with viscous oil may be used in the recovery of the oil from subterranean reservoirs, pipelining the oil to refineries, and in upgrading the oil at refineries. Adding solvent to oil can reduce its viscosity and thus facilitate production and pipelining. Adding certain solvents may also cause low value asphaltic components to precipitate and thus facilitate their separation thus generating an upgraded oil which can simplify later refining. There is a need for an improved method for recovering solvent from fluids produced in solvent-dominated recovery processes so as to optimize the entire production-pipelining-refining chain.